Species ca. 140 (26 in the flora): North America, Mexico, West Indies, Central America, South America, Europe, Asia, Africa, Australia.

For this treatment the segregate Orthodicranum is not recognized. Whether to recognize that genus or not has been debatable for years. W. L. Peterson (1979) listed the following six characters that he considered important in separating it from Dicranum: (1) capsules straight vs. curved; (2) capsules smooth to slightly wrinkled vs. ribbed; (3) alar cells 1-stratose vs. 2-stratose; (4) peristome teeth relatively narrow (ca. 60 µm) vs. relatively wide (70-95 µm or more); (5) specialized asexual reproduction by broken leaf tips or flagellated branches common vs. rare; (6) specialized habitat of rocks and wood vs. habitat of wood or rock rare, usually on soil or humus. The species placed in Orthodicranum by him as well as by other bryologists are D. flagellare, D. fulvum, D. montanum, D. tauricum, and D. viride. Dicranum fragilifolium is another species in the flora area that also has been placed in Orthodicranum by some bryologists (e.g., J. Podpera 1954). The problem with recognizing that genus is that some of the members otherwise remaining in Dicranum share one or more of the six character states Peterson outlined for the segregate genus. Dicranum fragilifolium and D. rhabdocarpum are two of the species that commonly have some of the characters of Orthodicranum and some of those of Dicranum. Other species in Dicranum less commonly have characters of both genera. If for no other reason but the sake of utility it is more practical at this time to leave all the species in one genus so they can be keyed out together and compared more readily. Perhaps when a world monograph of Dicranum is done it will become more evident whether it is important to recognize Orthodicranum and perhaps even other segregate genera.

Leaf cross sections are necessary to observe cell features of the costa and laminal cells. The costa stereid and guide cells, the adaxial and abaxial epidermal cells, the number of layers of alar and laminal cells, and the bulges in the cell walls between the laminal cells are all observable in cross section. These characters are extremely important because they can reliably differentiate many species of Dicranum. The leaf cross section characters are usually less variable and less influenced by the environment than other gametophytic characters, such as leaf habit, shape, margins and costa length characters, and are utilized to a great extent since they are considered much more dependable in species identification than some of the other characters in the genus.

Costa with stereid bands, although sometimes weak, with 2-3 layers of cells above and below the guide cells in the basal part of the leaf; alar cells 1- or 2-stratose; capsule straight and erect or arcuate

Leaf cells smooth or weakly papillose in distal half of leaf; costa with stereid bands in distal part of leaf as well as below, adaxial epidermal layer of cells noticeably enlarged and differentiated from stereid cells below; capsule not strumose, solitary; across North America